Encode integer variables so that they have a non-standard
data representation. The goal is for a variable's real value (and
the values of intermediate expressions used to compute it) to never
be revealed, until it is printed or otherwise escapes the
program. For example, an integer variable v could be
replaced with:
v' = a*v + b
where
Tigress might produce the following: A typical invokation of this transformation lists a collection of local
variables and formal parameters, and global variables: These variables should all be integers, pointers to integers, arrays of integers, or combinations
of these. In the example above, If you ask Tigress to encode a variable This transformation is based on ideas from several Cloakware/IRDETO papers and patents:a is a random odd integer and b a
random integer. For example, given this programint main () {
int arg1 = ...
int arg2 = ...
int a = arg1;
int b = arg2;
int x = a*b;
printf("x=%i\n",x);
}
a = 1789355803 * arg1 + 1391591831;
b = 1789355803 * arg2 + 1391591831;
x = ((3537017619 * (a * b) - 3670706997 * a) - 3670706997 * b) + 3171898074;
printf("x=%i\n", -757949677 * x - 3670706997);
Usage
--Transform=EncodeData \
--GlobalVariables='g1,g2' \
--LocalVariables='fun1:L1,L2;fun2:L3' \
--EncodeDataCodecs=poly1
g1 may be an int, L1 an int*,
L2 an array of ints, and L3 an array of pointers to ints.
Option Arguments Description
--Transform
EncodeData
Replace integer variables with a different encoding. Use --GlobalVariables and --LocalVariables to specify the variables that should be transformed. In addition to the variables specifed, any other variables that are related through aliasing will be transformed. Only integer variables, arrays of integers, and pointers to integers are currently supported. Avoid structs, since our alias analysis algorithm conflates all fields.
--EncodeDataCodecs
poly1, xor, add, *
Comma-separated list of the kinds of codecs that may be used. Only poly1 currently makes sense; avoid the others. Default=poly1.
Issues
x, then all variables
related to x through aliasing must also be encoded.
In cases where our alias analysis algorithm isn't precise enough, encoding
will fail at transformation time. For large programs, the alias analysis
routine may take a very long time.
References